The most common failure is of the electrode itself- it becomes internally grounded. You can pull the spark wire from the igniter module and listen for the snap to check. If it is that, often simply removing the electrode, wiping it down with a paper towel soaked in silicone lube, and lightly sanding the wire part will make it operational again.
Other than that- the revised wiring doesn't use the blue wire- it hooks the igniter module to the gas valve, so that it always has power if the gas valve is open. It also moves the grounds around. You can see the revised wiring at
http://bryantrv.com/docs2/docs/R704B.pdf.
